The present invention relates to an electromagnetic coupling apparatus provided with rubber vibration insulators for preventing attraction noise and screaming noise from being generated when an armature is magnetically attracted to and frictionally engaged by a rotor and, more particularly, to prevention of falling off of the rubber vibration insulators.
Of conventional electromagnetic coupling apparatuses, in an electromagnetic clutch for an automotive air-conditioning system, a stopper plate formed as an extension of the flange portion of an armature hub mounted on the rotating shaft of a compressor is fixed to the flange portion of the armature hub together with the proximal end portions of leaf springs with caulked rivets.
A plurality of rubber stoppers for setting the initial deflection of the leaf springs are mounted on the stopper plate at distances in the circumferential direction, and the armature to which the free end portions of the leaf springs are fixed is abutted against the rubber stoppers by the spring force (restoring force) of the leaf springs. Furthermore, a plurality of recessed portions are formed in the stopper plate at distances in the circumferential direction, and the distal ends of headed members (rivets), having trunk portions extending through through holes formed at the centers of rubber vibration insulators accommodated in the recessed portions and through holes formed at the bottom portions of the recessed portions, are caulked in stepped through holes formed in the armature. The rubber vibration insulators are interposed between the head portions of the headed members integrally formed with the armature and the bottom portions of the recessed portions of the stopper plate. Recessed portions for accommodating the rubber vibration insulators may be formed in the head portions of the headed members (see Japanese Utility Model Laid-Open No. 1-136727).
In the electromagnetic clutch having the above structure, when an electromagnetic coil in a field core supported by the compressor is energized, the armature is magnetically attracted to the rotor rotatably supported by the compressor, so that rotation of the rotor coupled to the pulley of the engine through a belt is transmitted to the rotating shaft of the compressor. When the electromagnetic coil is deenergized, the magnetic flux disappears, so that the armature is separated from the rotor by the spring force of the leaf springs and is moved backward until it is abutted against the rubber stoppers. As a result, transmission of rotation to the rotating shaft of the compressor is disconnected. In the conventional electromagnetic clutch, when this operation is repeated, every time the armature is magnetically attracted to the rotor, the rubber vibration insulators are compressed by the headed members integrally formed with the armature. Thus, the magnetic attraction noise generated between the armature and the rotor and the screaming noise generated by frictional engagement that takes place until the armature and the rotor are rotated integrally are prevented.
The rubber vibration insulators of the conventional electromagnetic clutch are compressed in the recessed portions of the stopper plate as the armature is magnetically attracted to the rotor. Also, deformation of the rubber vibration insulators is suppressed by the inner circumferential walls of the recessed portions of the stopper plate, so that the through holes at the centers of the rubber vibration insulators will not be enlarged by the centrifugal force to let the rubber vibration insulators to fall off from the headed members. In general, however, the space between the stopper plate and the armature is designed to about 2 mm to be equal to the thickness of the rubber stoppers that are provided to obtain the initial deflection of the leaf springs. To form recessed portions having a sufficient depth for accommodating the rubber vibration insulators, for example, the proximal end portions of the leaf springs, a spacer for increasing the space between the stopper plate and the armature, and the stopper plate are overlaid on the flange portion of the armature hub, and are fixed integrally with a rivet which is caulked.
In this structure, a gap must be provided between the armature abutted against the rubber stoppers by the leaf springs and the recessed portions of the stopper plate, and this gap must be set more or less largely in consideration of elastic deformation of the rubber stoppers. Then, the size of the electromagnetic coupling apparatus in the axial direction is increased. In addition, the thickness of the rubber stoppers is also increased, leading to many design modifications of the existing electromagnetic coupling apparatus, which is not economical.
The air gap between the armature and the rotor is generally designed to about 0.3 to 0.6 mm. Every time the armature is magnetically attracted to the rotor, the rubber vibration insulators are compressed and elastically deformed. If the entire inner circumferential surfaces of the cylindrical rubber vibration insulators are fitted on the trunk portions of the headed members, as in the conventional electromagnetic clutch, the outer circumferential surfaces of the elastically deformed rubber vibration insulators are sandwiched between the ridges of the openings of the recessed portions and the head portions of the headed members, or the end faces of the rubber vibration insulators close to their centers bite into the edges of the openings of the through holes formed in the bottom portions of the recessed portions. Then, cracks are formed in the rubber vibration insulators, thereby degrading the durability of the rubber vibration insulators.